1. Field of the Invention
The present invention relates to a copper powder and copper paste used for forming a conductor on a ceramic electronic component.
2. Description of the Related Art
A ceramic electronic element generally has conductive patterns or conductors in or on a ceramic body. The conventional copper pastes used for producing such a ceramic electronic element are prepared by dispersing copper powder and glass frit in organic vehicle which consists of resin(s) and solvent. The copper paste is applied or printed onto a ceramic body, dried and then sintered under a weak oxidizing atmosphere. Typically, a nitrogen gas containing oxygen at about 100 ppm is employed in order to hasten burning the organic vehicle and eliminating contamination of carbon in the produced conductive patterns or conductors.
On the other hand, it is important to prevent the copper powder in a copper paste from being oxidized since the oxidation of the copper powder degrades the characteristics of the produced conductive patterns, such as adhesive properties and solderability and increases the resistivity thereof. Therefore, the conventional art has proposed various methods to subject copper powder used for conductive pastes to an anti-oxidizing treatment. For example, Japanese Laid-open Patent Publication Nos. 5-195005 and 5-195260 disclose methods to coat copper powder with a boric acid film acting as an anti-oxidizing film by immersing copper powder in boric acid.
However, the conventional art has the following drawbacks. Specifically, it is difficult to coat the entire outer surfaces of copper powder with boric acid perfectly. As a result, the copper powder prepared by the aforementioned conventional methods may be likely to be oxidized by oxygen present in the sintering atmosphere and portions of the outer surfaces of the copper powder are not covered with the boric acid. In the case where the boric acid film is made thick so as to perfectly cover the entire outer surfaces of the copper powder therewith, there arises another problem in that the copper paste shows poor adhesiveness to the ceramic due to the thick boric acid film.